1. Field of the Invention:
The invention relates to a printing apparatus such as a laser printer, a LED printer, and the like, which forms an image on a sheet of copy paper.
2. Description of the Prior Art:
A variety of office machines including computers have been developed recently and the number of them introduced to each office has been increasing. The more machines one office has, the more difficult it becomes to find room for them. In general, office machines such as computers are placed on desks with their peripheral devices, which occupy large areas placed around these desks. This makes it difficult for workers to move smoothly around them while they are working, resulting in reduced labor efficiency in the office. Therefore, such office machines should be miniaturized so that they do not occupy such large areas.
Printing apparatuses such as laser printers or LED printers, which form an image by electrostatic printing, are often used as the peripheral devices for the office machines, i.e., computers, word processors, or the like.
With a conventional copying apparatus or laser printer, for example, a releasable paper cassette is connected to one side of its main body or housing in such a manner that the cassette protrudes from the housing. A pivoting paper supply roller is disposed above the end of the paper cassette so that the roller is in contact with the paper within the cassette. When the paper supply roller rotates, a sheet of copy paper is transported into a paper conveyer within the housing. The paper conveyer is provided with a photosensitive means, a developing device, a fixing device, and the like. A toner image formed on the photosensitive means by the developing device is transferred onto the sheet of copy paper which has been supplied to the paper conveyer. Then, the transferred toner image is fixed onto the sheet by the fixing device, and the resulting printed-paper is discharged into a paper receiving tray.
The paper receiving tray is usually disposed on the other side of the housing, which is on the opposite side to that having the paper cassette. In this way, with a conventional printing apparatus, the paper cassette and the paper receiving tray usually protrude from the opposite sides of the housing, so that the whole printing apparatus occupies a large area in an office.
Japanese Laid-open Patent Publication No. 63-236052 discloses a printing apparatus in which a face-down tray functioning as the paper receiving tray is disposed on the top of the housing so that the whole printing apparatus occupies a smaller area. However, it still has a paper cassette protruding from the housing, making the whole apparatus inefficient in its use of space.
Moreover, with a conventional printing apparatus, regardless of the position of the paper receiving tray, a paper exit through which sheets of copy paper are discharged out of the housing is disposed on the opposite side of the housing from the paper cassette. Thus, it is difficult to observe the quantity of the paper remaining in the paper cassette and see if the printed paper sheet has come out well at the same time.
A conventional printing apparatus is also disadvantageous in that it is difficult to supply new sheets of copy paper into the paper cassette, to remove a paper cassette or to take out discharged copy sheets.
In general, the paper cassette is provided with a cover which prevents dust or other foreign substances from entering the paper cassette. Attachment of such a cover to the paper cassette naturally means that one component is added to the whole apparatus, resulting in an increase in production cost.
The paper cassette is usually connected to the housing in such a way that it can be removed when new copy sheets are to be supplied. With such an arrangement, additional components for releasably mounting the paper cassette to the housing are required, resulting in an increase in production cost.
A conventional printing apparatus is generally provided with a door which opens into the housing. When a paper conveyer within the housing is jammed with sheets of copy paper, the door can be opened to expose the paper conveyer so that the jammed paper sheets can be removed. With such an arrangement also, additional components, i.e., the door, mounting members for mounting it to the housing, and the like, are required for the whole apparatus, resulting in a complicated structure, which causes an increased production cost of the apparatus.
The paper supply roller for transporting copy sheets from the paper cassette into the housing is usually mounted to the housing. Thus, additional components such as a supporting member or the like for mounting the roller to the housing are required for the production of the whole printing apparatus, resulting in a complicated structure, which causes an increased production cost.
A conventional printing apparatus is also provided with a pair of paper discharge rollers for transporting printed sheets out of the housing. One of the paper discharge rollers is usually attached to a mounting member disposed along the paper conveyer, and the other roller is usually attached to a pivoting supporting member connected to the housing. When the space between the two paper discharge rollers is jammed with copy sheets, the supporting member rotates upward so that the jammed sheets can be removed. With such a printing apparatus, however, since one of the paper discharge rollers is pivotably connected to the housing by means of the supporting member, additional components such as the supporting member and the like are required to be mounted within a printing apparatus. This causes a complicated structure, resulting in an increased production cost of the whole apparatus.
A conventional printing apparatus is also provided with a pair of guide-wall members for guiding a sheet of copy paper transported by the paper discharge rollers to a paper exit. The two guide-wall members face each other and the space therebetween functions as a part of the paper conveyer. These guide-wall members are both attached to the housing, so that additional components such as mounting members or the like for mounting these two guide-wall members to the housing are required. This causes a complicated structure, resulting in an increased production cost.
A laser printer in which a semiconductor laser is used to form a latent image on the photosensitive means has been developed as a printing apparatus. Such a laser printer is usually provided with a reflecting means such as a mirror for reflecting the laser beams emitted from the laser so as to illuminate the photosensitive means. The reflecting member is usually mounted in the housing, so that the additional components such as supporting members and the like for supporting the reflecting means within the housing are needed. This causes a complicated structure, resulting in an increased production cost.
With a printing apparatus, it is necessary to detect the size of the copy paper to control the quantity of toner. For example, Japanese Laid-open Patent Publication No. 60-61426 discloses a paper size detecting device for detecting the size of a copy sheet. With a printing apparatus, it is also necessary to check that the paper cassette is properly placed in the housing. If the printing apparatus is operated without the paper cassette being properly placed, the apparatus may be jammed with copy sheets or may be broken. Thus, a paper cassette checking means for checking that the paper cassette is properly placed is required for a printing apparatus. With a conventional printing apparatus, the above-mentioned paper size detecting device and paper cassette checking means are separately disposed within the housing, so that additional components such as mounting members or wirings are required for these two devices. This causes a complicated structure, resulting in an increased production cost.